1. Field of the Invention
The present invention relates to an image processing apparatus and image processing method for representing inputted image data by printing and non-printing of dots. In particular, the present invention relates to an image processing method for, in the case where inputted image data is binary data, performing printing with binary data that achieves dot arrangement appropriate for a printing apparatus.
2. Description of the Related Art
In recent years, a printing apparatus such as an inkjet one is compatible with pieces of input image data in various formats. For example, in the case of outputting a photograph, a poster, or the like, multivalued data photographed by a digital camera, such as RGB data, serves as the input image data for the printing apparatus. On the other hand, in the case of using the printing apparatus for the purpose of proving a print or the like, screened Tiff data (binary data) having been subjected to RIP (Raster Image Processor) serves as the input image data.
In the case of inputting RGB multivalued data, an image processing apparatus performs color conversion of the multivalued data to multivalued data (e.g., CMYK data) corresponding to ink colors used by a printing apparatus, and then converts to binary data corresponding to resolution of the printing apparatus. In this case, a method that performs multivalued quantization to the multivalued data having a smaller number of gradations (e.g., 5-values) than that of the inputted multivalued data, and then with use of a dot arrangement pattern that specifies printing or non-printing for each of pixels corresponding to the resolution of the printing apparatus, converts to the binary data is used.
In such a dot arrangement pattern, dot arrangement convenient for the printing apparatus can be prepared. Also, for the same multivalued quantized value, a plurality of dot arrangement patterns among which positions of printed pixels (dots) are made different is prepared, and depending on any of various conditions, from among the plurality of dot arrangement patterns, one can also be selected. Specifically, for example, to prevent a bias from occurring among the numbers of times individual printing elements print dots, or between the numbers of times of printing during forward and backward scans, the plurality of dot arrangement patterns can be sequentially selected.
Japanese Patent Laid-Open No. 2000-141617 discloses a method that, by randomly selecting one of a plurality of dot arrangement patterns on the basis of a random number having a predetermined bit number, avoids unevenness, stripes, or pseudo contours of an image caused by characteristics of a printing apparatus main body.
On the other hand, Japanese Patent Laid-Open No. 2002-29097 discloses a dot arrangement pattern and a method for selecting the dot arrangement pattern that, in the case of printing an odd raster and an even raster by different nozzle arrays, or printing an odd column and an even column during different scans, prevents a bias in the number of printed dots from occurring between the scans or the rasters.
By employing the method disclosed in Japanese Patent Laid-Open No. 2000-141617 or Japanese Patent Laid-Open No. 2002-29097, even in the case where conveyance unevenness specific to a printing apparatus, or print position displacement specific to a print head is present, dot arrangement patterns that prevent such an adverse influence from being noticeable can be prepared and order of the patterns can be controlled.
However, in the case where the image data inputted to the printing apparatus is binary data, arrangement of printed dots is already specified by the binary data. Accordingly, dot arrangement that can deal with an adverse influence specific to a printing apparatus as disclosed in Japanese Patent Laid-Open No. 2000-141617 or 2002-29097 cannot be achieved on a print medium, and therefore an adverse influence on an image, such as density unevenness, stripes, or granular feeling may be caused.